1. Field of the Invention
The present invention relates to a bump forming method and apparatus, and in particular, relates to a method and apparatus by which when bumps are formed at specific positions on a main surface of a semiconductor substrate, no deformed bump is formed and no shape correcting process is necessary, thereby shortening the bump forming process and reducing the manufacturing cost.
2. Description of the Related Art
In conventional semiconductor devices such as ICs, LSIs, and VLSIs, bumps are formed at specific positions (typically, on bonding pads) on a silicon wafer (i.e., a semiconductor substrate) by compression-bonding of bump balls made of metal material, printing of metal paste, plating of metal layers, wire-bonding connection, or the like. One of these methods is selected according to the shape or size of the bumps to be formed. Here, the shape or size of the bumps necessary depends on the shape or thickness of the final device package.
Regarding the compression-bonding of bump balls, various methods have been developed. For example, a bonding head is used on which attraction holes for attracting bump balls are provided at specific positions so as to arrange attracted bump balls, and these arranged bump balls are compressed onto bonding pads provided on a silicon wafer (see Japanese Unexamined Patent Application, First Publication No. Hei 11-31697 (refer to pp. 4-5, and FIG. 1), or the etc.).
Generally, when a relatively large number of bump balls are compression-bonded, the number of bonding pads on a silicon wafer may be several hundred thousand. In this case, the area of the silicon wafer is divided into sections in a manner such that the number of bump balls for each section is equal to or smaller than a specific number, and a set of bump balls for each section are compression-bonded all together onto the section.
In conventional compression-bonding of bump balls, the bonding head must be processed with a specific processing accuracy so as to form a large number of attraction holes at specific positions on an attraction face, where the number of the attraction holes is determined depending on the size and number of the bump balls to be attracted. Such processing is not easy.
When the bump balls are compression-bonded all together onto a large number of bonding pads, the force for attracting the bump balls may be reduced, and as a result, it is difficult to compression-bond bump balls all together.
In addition, when bump balls are attracted to the attraction holes, the bump balls may be deformed. In this case, the deformed shapes must be corrected in a subsequent process. Such correction of the shapes of the bump balls is also performed by compression-bonding; thus, two compression-bonding processes must be performed.
If the type of the semiconductor device to be manufactured is changed, the bonding head must be changed according to the type. Here, the bonding head is moved with respect to the silicon wafer; thus, the movement of the bonding head must also be highly accurate and precise. Therefore, when the bonding head is changed, the position or the like of the bonding head must be adjusted again; thus, it is not easy to change the bonding head.